In a typical wireless communication network, wireless devices, also known as wireless communication devices, mobile stations, stations (STA) and/or user equipments (UE), communicate via a Radio Access Network (RAN) to one or more core networks (CN). The RAN covers a geographical area which is divided into service areas or cell areas, with each service area or cell area being served by a radio network node such as a radio access node e.g., a Wi-Fi access point or a radio base station (RBS), which in some networks may also be denoted, for example, a “NodeB” or “eNodeB”. A service area or cell area is a geographical area where radio coverage is provided by the radio network node. The radio network node communicates over an air interface operating on radio frequencies with the wireless device within range of the radio network node.
A Universal Mobile Telecommunications System (UMTS) is a third generation (3G) telecommunication network, which evolved from the second generation (2G) Global System for Mobile Communications (GSM). The UMTS terrestrial radio access network (UTRAN) is essentially a RAN using wideband code division multiple access (WCDMA) and/or High Speed Packet Access (HSPA) for user equipments. In a forum known as the Third Generation Partnership Project (3GPP), telecommunications suppliers propose and agree upon standards for third generation networks, and investigate enhanced data rate and radio capacity. In some RANs, e.g. as in UMTS, several radio network nodes may be connected, e.g., by landlines or microwave, to a controller node, such as a radio network controller (RNC) or a base station controller (BSC), which supervises and coordinates various activities of the plural radio network nodes connected thereto. This type of connection is sometimes referred to as a backhaul connection. The RNCs and BSCs are typically connected to one or more core networks.
Specifications for the Evolved Packet System (EPS), also called a Fourth Generation (4G) network, have been completed within the 3rd Generation Partnership Project (3GPP) and this work continues in the coming 3GPP releases, for example to specify a Fifth Generation (5G) network. The EPS comprises the Evolved Universal Terrestrial Radio Access Network (E-UTRAN), also known as the Long Term Evolution (LTE) radio access network, and the Evolved Packet Core (EPC), also known as System Architecture Evolution (SAE) core network. E-UTRAN/LTE is a variant of a 3GPP radio access network wherein the radio network nodes are directly connected to the EPC core network rather than to RNCs. In general, in E-UTRAN/LTE the functions of an RNC are distributed between the radio network nodes, e.g. eNodeBs in LTE, and the core network. As such, the RAN of an EPS has an essentially “flat” architecture comprising radio network nodes connected directly to one or more core networks, i.e. they are not connected to RNCs. To compensate for that, the E-UTRAN specification defines a direct interface between the radio network nodes, this interface being denoted the X2 interface. EPS is the Evolved 3GPP Packet Switched Domain. FIG. 1 is an overview of the EPC architecture. This architecture is defined in 3GPP TS 23.401 v.13.4.0 wherein a definition of a Packet Data Network Gateway (P-GW), a Serving Gateway (S-GW), a Policy and Charging Rules Function (PCRF), a Mobility Management Entity (MME) and a wireless or mobile device (UE) is found. The LTE radio access, E-UTRAN, comprises one or more eNBs. FIG. 2 shows the overall E-UTRAN architecture and is further defined in for example 3GPP TS 36.300 v.13.1.0. The E-UTRAN comprises eNBs, providing a user plane comprising the protocol layers Packet Data Convergence Protocol (PDCP)/Radio Link Control (RLC)/Medium Access Control (MAC)/Physical layer (PHY), and a control plane comprising Radio Resource Control (RRC) protocol in addition to the user plane protocols towards the wireless device. The radio network nodes are interconnected with each other by means of the X2 interface. The radio network nodes are also connected by means of the s1 interface to the EPC, more specifically to the MME by means of an S1-MME interface and to the S-GW by means of an S1-U interface.
The S1-MME interface is used for control plane between eNodeB/E-UTRAN and MME. The main protocols used in this interface are S1 Application Protocol (S1-AP) and Stream Control Transmission Protocol (SCTP). S1AP is the application layer protocol between the radio network node and the MME and SCTP, for example, guarantees delivery of signaling messages between MME and the radio network node.
In LTE-Rel-13 and LTE-Rel-14, latency reduction techniques are discussed and being standardized in 3GPP. Among others, a solution of allowing short Semi-Persistent-Scheduling (SPS) intervals and the possibility to skip UL transmissions when no UL data is available has been discussed.
With SPS in UL, the wireless device is configured with an UL grant, also referred to as SPS grant, indicated with a SPS-Radio Network Temporary Identifier (RNTI), which is valid during the SPS-intervals or occasions preconfigured over Radio Resource Control (RRC) signaling, e.g. every 10 ms, or every 1 ms. During SPS, certain things remain fixed for each allocation e.g. Resource Block (RB) assignments, Modulation and Coding Scheme (MCS), etc. When UL data is available, the wireless device can use the configured UL grant for transmission. According to legacy behavior, the wireless device sends a padding transmission on the configured UL grant, if no data is available. In Rel-14 it is standardized to allow skipping of these padding transmissions.
Retransmissions in SPS can be handled by non-adaptive Hybrid Automatic Repeat Request (HARQ) retransmissions in occasions where an SPS grant, i.e. the preconfigured UL grant, is not valid. This possibility does not exist for 1 ms period, since the SPS grant is valid in all subframes. Retransmissions can also be explicitly handled by the radio network node through adaptive HARQ operation. In this case the radio network node sends another Physical Downlink Control Channel (PDCCH) UL grant to the wireless device, indicated to resources of the SPS interval, triggering an adaptive retransmission by the wireless device. Using the SPS grant for retransmissions may in some cases limit the performance of the wireless communication network.